Specialized equipment is used within airports for refueling airplanes. The fuel carriers which are commonly used to transport fuel on highways from the producer to the airport (referred to herein as "highway trucks") are not normally permitted to drive in the often narrow and congested areas in which the airplanes are serviced and fueled. Special "refueler" vehicles are used to navigate through the airport and provide the fuel to the airplanes (such as the "Rampmaster" trucks sold by General Transervice, Inc. of Coatesville, Pa.). These refueler vehicles have characteristics that render them particularly well suited for navigating turns in airports and avoiding accidental contact with airplanes.
It is common for airplane fuel to be delivered to an airport by highway trucks capable of transporting about 7700 gallons of fuel each. The fuel from the truck is typically emptied into an in-ground storage tank (which may contain anywhere from 10 to 30 thousand gallons), via a standard low pressure transfer hose suitable for gravity drop.
Major airports are frequently constructed to have large-capacity above-ground supply systems for aircraft fuel, referred to herein as "fuel farms". The planes may also be refueled by way of hydrants located below the airport ramp. The hydrants are equipped with flow-control valves under the control of the operator to refuel the operator's vehicle (which is referred to as a "hydrant cart".).
Airplanes may also be fueled via truck tankers, by transferring fuel farm fuel into the specialized refueler vehicles. Special control systems have been used to monitor the fuel transfer from the fuel farm to the refueler.
One such control system is the "INTELLICHECK.TM." monitoring system manufactured by Scully Signal company. The monitor system is used in the fuel farm to monitor the fuel transfer, and cut off the pressurized pump flow out from the fuel farm if the monitor determines that the refueler is filled. The refueler has one or more sensors positionable at the top of the refueler tank which provide input signals to the monitor system. These sensors may, for example, be of the wet probe type (which uses an electronic field) or an optical sensor.
The refueler may have its own safety cutoff for the fuel flow, operating independently of the fuel farm's electronic control system. For example, the above-mentioned "Rampmaster" trucks sold by General Transervice, Inc. of Coatesville, Pa. include jet level sensors, such as those manufactured by the Whittaker Company of North Hollywood, Calif. The jet level sensor normally permits a pressurized jet of fuel to pass from an inlet to an outlet of the jet level sensor, if the fuel level in the refueler tank is below the height of the jet level sensor. The flow from the jet level sensor outlet is used to operate the pilot of a normally opened valve that admits fuel to the refueler tank. If, however, the tank fuel level rises to the height of the jet level sensor, the sensor fills up, and the fuel within the sensor disperses the pressurized jet. Thus, the fuel leaves the sensor at a low pressure; the pilot flow pressure falls below that required to maintain the refueler tank valve in the open position, and the tank valve closes to prevent overflowing.
Airports have been very reluctant to allow any direct transfer of fuel from the highway vehicle to the airport refueler, primarily because of safety and environmental concerns related to the possibility of spillage. The airports have been reluctant to rely on the jet level sensors normally installed in the trucks. For example, a spill could occur, creating a hazardous condition if (1) the refueler tank fuel receiving valve becomes frozen in the open position, (2) the airport refueler fills up, and (3) the highway truck continues to pump the fuel. Another concern is that the hose connecting the highway truck to the airport refueler could rupture and leak or spill fuel on airport surfaces. As a result, direct transfer of fuel from a highway truck to an airport refueler truck has seldom been permitted by airports.
Consequently, the two step procedure of delivering fuel from the highway truck to the fuel farm, and then loading the fuel from the fuel farm to the refueler vehicle remains in use. This two step fuel transfer process is time consuming and expensive.